The invention relates to an envelope flap moistener. Envelope flap moisteners are typically used for moistening one or more strips of adhesive material such as arabic gum on a flap of an envelope prior to closing the flap in an inserting apparatus for inserting postal items into the envelope, moistening the strips on the envelope flap and closing the envelope flap. Such envelope flap moisteners typically have an envelope transport track. An envelope is transported along the envelope track such that the flap to be moistened and closed is passed along a moisture transfer member. Moisture is transferred from the moisture transfer member to the adhesive material, which becomes to some extent liquefied and sticky when water is applied thereto. Then the flap is mechanically closed and the adhesive sticks to the body of the envelope and is to some extent absorbed by the envelope body, so that a strong joint between the flap and the body of the envelope is obtained. In practice, the joint is generally so strong that the flap cannot be disconnected from the envelope body without damaging the envelope. Thus, the adhesive also constitutes a sealing material.
During operation of inserting apparatus, the dosage of liquid (generally simply water) should be such that the adhesive is moistened sufficiently to obtain a sufficiently strong bond between the body and the flap of the envelope, but not excessively to avoid excessive wrinkling of the envelope or even damage to the contents of the envelope. When the apparatus is operating in an essentially steady state condition, moistening a fairly constant number of envelope flaps per unit of time, providing a proper dosage of liquid is generally no problem. However, when the apparatus is started after having been out of operation for a longer period, e.g. more than an hour or several hours, it is often a problem to ensure quickly that the liquid is properly dosed as of the first envelopes of a series of mail pieces.